Charges of Subatomic Particles

Introduction

The plus and minus signs in atomic diagrams stand for measurable electrical properties. They can be used as relative counting units or converted into coulombs. Learning to move between these descriptions helps prevent errors such as treating a 2+ ion as carrying two coulombs or giving a neutral atom a neutral nucleus.

Core explanation

Use e for the positive magnitude of elementary charge. For school calculations, e ≈ 1.60 × 10⁻¹⁹ C. A proton carries +e, an electron carries −e and a neutron has zero net electric charge. Relative charges +1, −1 and 0 simply express those values in units of e.

If a particle contains p protons and Nₑ electrons, its total charge is Q = (p − Nₑ)e . The subtraction is algebraic. More electrons than protons give a negative result; fewer electrons give a positive result. Neutron count does not appear because multiplying it by zero adds no charge.

Nuclear charge and whole-particle charge differ. A nucleus with thirteen protons always carries +13e. An aluminium atom with thirteen electrons has total charge zero, whereas Al³⁺ has ten electrons and total charge +3e. The nucleus is the same in both descriptions.

Electron transfer redistributes charge rather than creating it. If a neutral atom loses one electron, the remaining ion has charge +e and the separated electron has charge −e. Together they still have total charge zero. Describing only the ion without the emitted electron can hide this conservation.

It is also essential to name the object being counted. A molecule, an ion, an atom and a collection of particles can each have a net charge. Three separate singly positive ions have total charge +3e, but they do not become one triply positive atom merely because their charges add.

Formulae

Relative net charge = proton count − electron count.

Charge in coulombs = relative net charge × e.

Using rounded values: e ≈ 1.60 × 10⁻¹⁹ C.

Step-by-step reasoning

1. Write proton and electron counts explicitly. 2. Subtract electron count from proton count and retain the sign. 3. Report that integer if relative charge is requested. 4. Multiply by e only when the answer must be given in coulombs.

Visual explanation

Pair every proton plus sign with one electron minus sign. Cross out each balanced pair in the charge tally, not in the physical atom. Any remaining plus or minus signs show the relative net charge. Leave neutron symbols outside this charge bookkeeping.

Real-world analogy

A balance sheet with equal credits and debits has a zero net balance even though many entries remain. The cancellation concerns the total, not the disappearance of the entries. Atomic neutrality similarly leaves all the charged constituents present.

Real-world example

In an ionic crystal, positive and negative ions combine in proportions giving overall neutrality. Magnesium ions carry +2e while chloride ions carry −e, so two chloride ions balance one magnesium ion. Charge counting therefore helps explain the formula MgCl₂.

Why?

Why does losing a negative electron make a particle more positive? Removing a negative contribution increases the algebraic sum. The proton count need not increase. The change is in the balance of existing charges, not the creation of additional positive constituents.

Common misconception

“An ion marked 3+ contains three protons.” The notation gives the excess of proton charge over electron charge. Al³⁺ contains thirteen protons and ten electrons, not a nucleus with only three protons.

Worked example

A particle has sixteen protons, eighteen electrons and sixteen neutrons. Relative charge is 16 − 18 = −2. Using e ≈ 1.60 × 10⁻¹⁹ C, Q = −3.20 × 10⁻¹⁹ C. The neutrons affect its isotope but do not alter this charge calculation. The particle is a sulfide ion, S²⁻.

Quick check

1. What net charge remains when one proton's charge and one electron's charge are added? Answer: Zero, because +e and −e are equal in magnitude and opposite in sign.

Exam focus

Keep ion charge as a superscript in chemical notation and do not confuse it with a subscript atom count. In Ca²⁺ the 2 describes charge; in Cl₂ it describes two chlorine atoms in a molecule.

Advanced insight

The SI defines the elementary charge exactly as 1.602176634 × 10⁻¹⁹ C. Rounded classroom values are chosen for manageable arithmetic. More digits improve numerical precision only when the rest of the supplied information warrants that precision; rounding does not change the charge-counting rule.

Summary

Relative charge counts elementary-charge units, while coulombs provide the SI measure. Protons contribute +e, electrons −e and neutrons zero. The difference between proton and electron counts gives ion charge, and including transferred electrons preserves total charge.

Practice questions

1. A particle has twelve protons and ten electrons. Give its relative charge. Answer: +2, since 12 − 10 = 2. 2. Convert that charge into coulombs using e ≈ 1.60 × 10⁻¹⁹ C. Answer: +3.20 × 10⁻¹⁹ C. 3. Does the neutral atom of an element have zero nuclear charge? Answer: No. Its positive nuclear charge is balanced by an equal negative electron charge. 4. What balances the charge of one Ca²⁺ ion using chloride ions? Answer: Two Cl⁻ ions, whose combined charge −2e balances +2e.